In the photolithography process for manufacturing semiconductor devices and the like, an exposure apparatus is used that projects an image of a pattern on a photomask or reticle (hereinafter, reticle) through an optical system (i.e., a projection lens) and onto a wafer or glass plate and the like (hereinafter, wafer) coated with photoresist or the like. In recent years, the size of semiconductor devices have been growing larger, while at the same time the level of integration of these devices has been increasing. Accordingly, scanning-type exposure apparatuses are being developed in order to deal with the increased size and increased level of integration of semiconductor devices.
Along with the increased level of integration of semiconductor devices, there is also an increasing demand for more resolving power from the optical system. To satisfy this demand, it has become necessary to shorten the wavelength of the illumination light and to increase the numerical aperture (NA) of the optical system.
When the wavelength of the illumination light is shortened down to the ultraviolet, only limited types of glass materials are fit for use, depending on the absorption of the light. For wavelengths under 300 nm, only synthetic quartz glass (hereinafter, "quartz") and fluorite can presently be used for the glass material. Since the Abbe numbers of these glass types are not sufficiently different, it is difficult, in cases wherein the wavelength is less than 300 nm, to correct the various aberrations. This particularly true for chromatic aberration when the optical system comprises only refractive components (i.e., is dioptric).
On the other hand, since reflective systems have no chromatic aberration, various catadioptric optical system designs (i.e., designs that combine both reflective and refractive elements have been proposed. For example, Japanese Patent Application Kokoku No. Hei 7-117648, Japanese Patent Application Kokai No. Hei 6-300973, Japanese Patent Application Kokai No. Hei 5-88089, Japanese Patent Application Kokai No. Hei 3-282527, and PCT/EP95/01719 disclose catadioptric reduction optical systems, which include a beam splitter for diverting the optical path to input a light beam from and output a light beam to a reflective system.
In conventional catadioptric optical systems employing a beam splitter, such as those cited above, it is necessary that the beam splitter have a transmission-reflection surface to split the optical path, and to make the beam splitter prism-shaped to avoid generating asymmetric aberration. Nevertheless, the larger the prism-type beam splitter, the greater the risk that the resolving power will deteriorate due to the non-uniformity of the material comprising the prism.
Japanese Patent Application Kokai No. Hei 3-282527 discloses a catadioptric optical system which uses a polarizing beam splitter designed to prevent a loss in the quantity of light or the generation of stray light due to flaring and the like. However, a transmission-reflection film having a multilayer construction that transmits "p" polarized light and reflects "s" polarized light is needed on the transmission-reflection surface of the polarizing beam splitter. In addition, a 1/4-wave plate is essential to change the polarization state. As the optical elements like the polarizing beam splitter and the 1/4-wave plate become larger, manufacturing becomes extremely difficult, and the manufacturing costs required to achieve sub-quarter-micron resolving power become extremely large.